Abstract: A procedure and apparatus for transmitting binary messages in a serial communication bus, to which several transmitting stations are connected is disclosed. Each station is able to transmit a message when the bus is free, and is a signal collision situation when several stations attempt to transmit messages simultaneously, each station monitors the message which is passing through the bus and only the station which has the highest priority is allowed to go ahead and transmit its message while each station having a lower priority which, when transmitting a signal of a logic state assigned a recessive status, receives a signal of a logic state assigned a dominating status cancels its transmission attempt. All stations transmit a dominant signal with the same polarity by recognizing the polarity of the signal present in the bus and by sending the dominating signal with that polarity.